Many current irrigation systems utilize a combination of water emission devices or sprinklers coupled together by a system of irrigation pipes for delivering water to the sprinklers. In some environments, such as large scale irrigation of agricultural lands, the sprinkler system is principally above ground and is designed to be moved from one location to another. In other environments, the sprinkler system is principally installed under a ground surface, with an emission portion either co-located with the ground or designed to extend from a retracted position when the system is turned-on or activated.
As the systems installed within the ground are designed to be generally permanently installed, problems arise due to weather conditions. As is known, the water typically delivered by the sprinkler system expands when it freezes. The presence of fertilizer or other chemicals in the water is usually not sufficient to reduce the freezing point sufficiently, and most parts of the United States, for instance, experience winter air temperatures sufficient to freeze the water.
The entirety of the sprinkler system is not necessarily susceptible to the freezing. For instance, the irrigation pipes running generally parallel to the ground surface may be buried to a depth sufficient to be below a frost line, and vertical pipes, risers, and stems may be used with the emission device so that most water will drain downward when the system is de-activated. Such a design, however, may still fail to clear all of the water out, while requiring significantly more materials and labor to construct or repair.
The most common approach to preparing the irrigation system and sprinklers for impending cold weather is a winterization procedure in which high-pressured or compressed air is blown into the system. The air passes through the entire system and simultaneously dries the system and drives water from the pipes, sprinklers, and other controls.
Problems may arise from the winterization of sprinklers utilizing water-driven components. One type of sprinkler utilizes the flow of water therethrough to power the sprinkler, and many of these sprinklers are rotary sprinklers where the flow of water drives a motor or other mechanism for rotating a sprinkler head. Such sprinklers tend to present a great problem with winterization.
More particularly, these rotary sprinklers include a sprinkler head rotatably supported by a generally non-rotating housing. The non-rotating housing is often a riser which moves between a retracted position generally within a stationary housing buried in the ground surface and an extended position generally extended from the stationary housing to a position above the ground. Water flowing through the sprinkler typically contacts a water-driven structure such as a turbine having vanes so that a portion of the kinetic energy of the water is imparted to and rotates the turbine. A speed-reducing drive mechanism is operably coupled to the turbine and to the sprinkler head so that the high-speed rotation of the turbine (in the order of 1000-2000 revolutions per minute, though some operate as low as 500 revolutions per minute) is reduced so that the sprinkler head rotates at approximately ⅓ revolution per minute.
In the absence of any control and for a constant nozzle size, the rate of rotation for the turbine is generally dependent only on the pressure of the water flowing therethrough and on the size of a nozzle or orifice directing the water into the turbine. Under normal operating conditions, pressurized water flows through the sprinkler and causes the high rate of rotation for the turbine, which, as mentioned above, can be on the order of 1000-2000 revolutions per minute. Accordingly, when high-pressured air is injected through the system for winterization, an even higher resultant velocity is experienced by the turbine. Such higher velocity can be on the order of 40,000 revolutions per minute, and it is communicated through the sprinkler via the drive mechanism to the sprinkler head and to any other internal components.
Winterization using air creating this higher velocity can lead to damage in a rotary sprinkler. The principal concern comes from devices operating at speeds that are orders greater than for what the components were designed. This can result in unpredictable behavior, particular due to an eccentricity in a spinning component. Moreover, the friction and heat generated by the high-speed rotation has a negative effect on the components and can rapidly progress to failure by the components.
Currently, there are a number of mechanisms in existence for reducing the speed of a turbine or drive mechanism of a rotating sprinkler due to excessive flow. Bypass valves allow a portion of the water to pass directly through a stator structure instead of being focused at the turbine vanes. The velocity of the air against the turbine is generally dependent on the size of the orifice directing the air against the turbine and on a pressure drop across the stator. The reduction in pressure above the orifice due to the opening of a bypass valve may hold the pressure across the stator constant, but is simply not sufficient to lower the velocity of the air being directed at the turbine.
Another method for controlling rotation due to high flow utilizes centripetal force to shift two portions into frictional contact. Regardless of the efficiency or long-life of such a design, were this method relied upon during winterization, the amount of friction would be far in excess of expected levels for water operation. Accordingly, such friction devices serve to accelerate the failure of sprinklers that are winterized with pressurized air.
Accordingly, there is a need for a rotary sprinkler with a design improved for winterization.